Asphalt-based roofing materials, such as roofing shingles, roll roofing, and commercial roofing, have long been installed on the roofs of buildings to provide protection from the elements and to give the roof an aesthetically pleasing appearance. Typically, asphalt-based roofing material is constructed of a substrate such as a glass fiber mat or an organic felt mat, an asphalt coating on the substrate to provide a water barrier, and a surface layer of granules embedded in the asphalt coating. The granules help protect the asphalt from deterioration due to exposure to UV and IR radiation from the sun and direct exposure to the elements.
A common method of manufacturing asphalt-based shingles is to advance an endless sheet of the substrate material through a coater, which coats the sheet with heated liquid asphalt forming a hot tacky asphalt coated sheet. The asphalt coated sheet is typically then passed beneath one or more granule applicators, which dispense and apply protective and decorative surface granules onto at least selected portions of the moving asphalt coated sheet. A granule applicator may be as simple as a direct feed nozzle fed by an open hopper that is filled with granules or as complex as a servo controllable rotating fluted rollers and gate assemblies at the mouth of a granule hopper. The result can be an endless sheet of granule coated shingle stock, which can later be cut to size to form individual shingles, cut and rolled to form a rolled shingle, or otherwise processed into final shingle products.
In some shingle manufacturing processes, there is a need to deliver granules at intermittently timed intervals such that granules are applied to the asphalt coated sheet in patches that are spaced apart from each other and that are usually rectangular. For instance, patches of dark and light granules may be separated by patches of blended granules to form a decorative shingle. In such cases, several mechanisms have been used in the past to start and stop the delivery of granules in a controlled manner to produce the spaced patches of granules. Such mechanisms include, for instance, articulating gates at the outlet of a granule hopper and servo controlled fluted roll and gate assemblies at the outlet of a granule hopper. Fluted roll and gate assemblies may include one or more fluted rolls disposed along the outlet of a granule hopper. The fluted rolls can be rotated by server motors that, in turn, are controlled by a computer based controller. The gate assemblies also may be controlled by the controller. When a fluted roll is rotated and stopped by its servo motor, a metered charge of granules is drawn from the granule hopper and dropped onto the moving asphalt coated sheet below. In this way, intermittent patches of granules can be created on the asphalt coated sheet.
Prior systems and methods of depositing granules onto an asphalt coated sheet in shingle manufacturing have proven acceptable at lower production speeds (i.e. the speed of the asphalt coated sheet) but begin to exhibit problems at higher production speeds. For instance, as the speed of production increases, the edges and patterns of spaced granule patches on the asphalt become less and less defined. Eventually, the deposited patches of granules are so indistinct and distorted as to be unacceptable in appearance, coverage, and protection. Trailing edges in particular of a deposited patch of granules become more and more smeared out as the speed of production is increased and dispensed charges of granules exhibit unacceptable trailing patterns. As a result, granule delivery systems and methods typically used in the past have been practically limited to production speeds below about 800 feet per minute (FPM), even though other areas of shingle production are capable of moving much faster.
The above problem involves the decreasing ability to control precisely the rotation of fluted granule dispensing rolls, sometimes referred to as blend rolls, at higher production speeds. The volume of granules applied in a given application or “drop” typically is controlled by varying the gate position relative to the fluted roll and by varying the speed and duration of rotation of the fluted roll. Both may be controlled or varied as a function of production speed. To accomplish this, the servo and gate parameters are manipulated by the computer-based controller to control the amount of granules dropped in a given period of time. This, in turn, determines the appearance of patches of granules on the sheet. As production speed increases, the acceleration, duration, and deceleration of the fluted roll must be increased accordingly as well as gate position and other parameters because the same amount of granules must be dropped in a shorter interval of time.
The ability to control these parameters degrades as production speeds increase because of the need to apply more granules faster. This is accomplished by opening up the gate of the granule hopper to allow more granules to flow to the fluted roll and increasing the acceleration, speed, duration, and deceleration of the fluted roll. As production speeds increase more, the ability to control these parameters in such a way that acceptably distinct patterns of granules are deposited on the moving asphalt coated sheet below is lost. Plus, there is an inherent maximum speed at which servo motors can accelerate, rotate, and decelerate the rolls, which also limits production speed. Finally, the rate at which the granules fall is dictated by gravity and is substantially constant regardless of the rotation rate of a dispensing roll.
There is a need for a granule delivery system and method for use in shingle manufacturing that is capable of delivering a charge of granules at intermittently timed intervals onto a moving asphalt coated sheet with precision, definition, and controllability at higher manufacturing speeds of over 800 FPM and even over 1000 FPM. It is to the provision of such an apparatus and method that the present invention is primarily directed.